If the public wants it, “Manuals at no cost” could be made into law, I think. Certainly if restricted to something like “products with at least $x in revenue” for large enough x, it wouldn’t be that burdensome on manufacturers.

And unfair to Apple? Only if only Apple or a few companies would have to do that.

Also, for replacement parts, in some markets there already are regulations. See for example https://europa.eu/rapid/press-release_MEMO-04-215_en.htm for a discussion on finding the right balance between the protection of a car manufacturer’s designs and consumer’s rights to buy replacement parts made by third parties (I don’t know the end result of this discussion)